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DYNAMIC HOST CONFIGURATION PROTOCOL
Dynamic Host Configuration Protocol (DHCP) is a TCP/IP standard that reduces the complexity and administrative overhead of managing network client IP address configuration. Microsoft® Windows® 2000 Server provides the DHCP service, which enables a computer to function as a DHCP server and configure DHCP-enabled client computers on your network. DHCP runs on a server computer, enabling the automatic, centralized management of IP addresses and other TCP/IP configuration settings for your network's client computers. The Microsoft DHCP service also provides integration with the Active Directory ™ directory service and Domain Name System (DNS) service, enhanced monitoring and statistical reporting for DHCP servers, vendor-specific options and user-class support, multicast address allocation, and rogue DHCP server detection.
What Is DHCP?
DHCP simplifies the administrative management of IP address configuration by automating address configuration for network clients. The DHCP standard provides for the use of DHCP servers, which are defined as any computer running the DHCP service. The DHCP server automatically allocates IP addresses and related TCP/IP configuration settings to DHCP-enabled clients on the network.
Every device on a TCP/IP-based network must have a unique IP address in order to access the network and its resources. Without DHCP, IP configuration must be done manually for new computers, computers moving from one subnet to another, and computers removed from the network.
By deploying DHCP in a network, this entire process is automated and centrally managed. The DHCP server maintains a pool of IP addresses and leases an address to any DHCP-enabled client when it logs on to the network. Because the IP addresses are dynamic (leased) rather than static (permanently assigned), addresses no longer in use are automatically returned to the pool for reallocation.
The DHCP service for Microsoft Windows 2000 Server is based on Internet Engineering Task Force (IETF) standards. DHCP specifications are defined in Requests for Comments (RFCs) published by the IETF and other working groups. RFCs are an evolving series of reports, proposals for protocols, and protocol standards used by the Internet community. The following RFCs specify the core DHCP standards that Microsoft supports with its DHCP service:
• RFC 2131: Dynamic Host Configuration Protocol (obsoletes RFC 1541)
• RFC 2132: DHCP Options and BOOTP Vendor Extensions
The network administrator establishes one or more DHCP servers that maintain TCP/IP configuration information and provide address configuration to DHCP-enabled clients in the form of a lease offer. The DHCP server stores the configuration information in a database, which includes:
• Valid TCP/IP configuration parameters for all clients on the network.
• Valid IP addresses, maintained in a pool for assignment to clients, as well as reserved addresses for manual assignment.
• Duration of the lease offered by the server—the length of time for which the IP address can be used before a lease renewal is required.
A DHCP-enabled client, upon acceptance of a lease offer, receives:
• A valid IP address for the network it is joining.
• Additional TCP/IP configuration parameters, referred to as DHCP options.
Benefits of DHCP
Deploying DHCP on your enterprise network provides the following benefits:
• Safe and reliable configuration. DHCP minimizes configuration errors caused by manual IP address configuration, such as typographical errors, as well as address conflicts caused by a currently assigned IP address accidentally being reissued to another computer.
• Reduced network administration.
• TCP/IP configuration is centralized and automated.
• Network administrators can centrally define global and subnet-specific TCP/IP configurations.
• Clients can be automatically assigned a full range of additional TCP/IP configuration values by using DHCP options.
• Address changes for client configurations that must be updated frequently, such as remote access clients that move around constantly, can be made efficiently and automatically when the client restarts in its new location.
• Most routers can forward DHCP configuration requests, eliminating the requirement of setting up a DHCP server on every subnet, unless there is another reason to do so.
New Features
The Windows 2000 DHCP service provides the following new features:
• Enhanced performance monitoring and server reporting capabilities
New System Monitor counters have been added to Windows 2000 Server to specifically monitor DHCP server performance on your network. Additionally, DHCP Manager now provides enhanced server reporting through graphical display of current states for servers, scopes, and clients. For example, icons visually represent whether a server is disconnected, or if it has leased over 90 percent of its available addresses.
• Expanded support for multicast scopes and superscopes
Multicast scopes now allow multicast-aware applications to lease Class D–type IP addresses (224.0.0.0 to 239.255.255.255) for participation in multicast groups.
• Support for user-specific and vendor-specific DHCP options
This allows the separation and distribution of options for clients with similar or special configuration needs. For example, you might assign all DHCP-enabled clients on the same floor of your building to the same option class. You could use this class (configured with the same DHCP Class ID value) to distribute other option data during the lease process, overriding any scope or global default options.
• Integration of DHCP with DNS
A DHCP server can enable dynamic updates in the DNS namespace for any DHCP clients that support these updates. Scope clients can then use DNS with dynamic updates to update their computer name–to–IP address mapping information whenever changes occur to their DHCP-assigned address.
• Rogue DHCP server detection
This prevents rogue (unauthorized) DHCP servers from joining an existing DHCP network in which Windows 2000 Server and Active Directory are deployed. A DHCP server object is created in Active Directory, which lists the IP addresses of servers that are authorized to provide DHCP services to the network. When a DHCP server attempts to start on the network, Active Directory is queried and the server computer's IP address is compared to the list of authorized DHCP servers. If a match is found, the server computer is authorized as a DHCP server and is allowed to complete the system startup. If a match is not found, the server is identified as rogue, and the DHCP service is automatically shut down.
• Dynamic support for BOOTP clients
Dynamic BOOTP is an extension of the BOOTP protocol, which permits the DHCP server to configure BOOTP clients without having to use explicit, fixed-address configuration. This feature reduces administration of large BOOTP networks by allowing automatic distribution of IP address much the same way that DHCP does.
• Read-only console access to DHCP Manager
This feature provides a special-purpose local group, the DHCP Users group, which is automatically added when the DHCP service is installed. By adding members to this group, you can provide read-only access to information related to the DHCP service on the server computer. Using DHCP Manager, users in this group can view, but not modify, information and properties stored on the specified DHCP server.